When Security Essentials is running on your computer, it
automatically alerts you if it detects viruses, spyware, or other
potentially unwanted software. You can also set Security Essentials
to alert you if you run software that has not yet been analyzed,
and you can choose to be alerted when software makes changes to
your computer.

To set up Security Essentials alerts

Click Settings, and then click Real-time
protection.

Make sure the Turn on real-time protection
(recommended) check box is selected.

Select the check boxes next to the real-time
protections options you want to run, and then click Save
changes. If you're prompted for an administrator password or
confirmation, type the password or confirm the action.